This invention relates to an electrically-controlled actuator for moving a carriage in forward and reverse directions, particularly to a motor drive apparatus suitable for an automatic loading apparatus of a video disc player in which a protective casing for containing a video disc is drawn into the player and then the casing is pushed out therefrom, automatically.
A motor drive apparatus is available for moving a carriage in a given sequential order. In such apparatus a switching circuit for forwardly driving, reversely driving or stopping a motor is equipped. For the switching circuit a high reliability and a low power consumption are desired.
A conventional switching circuit for the above usage generally has a relay circuit with proper switches which designate the rotational direction and start/stop of the motor. Since the relay circuit requires a certain space, it is hard to reduce the size in the conventional circuit. Further, since the conventional one has many mechanical contacts, the operational reliability is low. Still further, the mechanical contacts are liable to generate sparks and electrical noises, and additionally, a relay is relatively expensive.
A semiconductor switch circuit may overcome the above-mentioned drawbacks of mechanical relays. One example of the semiconductor switch is disclosed in U.S. Pat. No. 3,896,358. This U.S. patent teaches that a switching circuit for forwardly driving, reversely driving or stopping the motor is obtained without a mechanical relay. In the circuitry of this U.S. patent, however, a complicated switching circuit is necessary for surely fixing the starting condition of motor actuation at the initial stage, e.g. the time of power ON.